CN111464149A

CN111464149A - Filter amplifier

Info

Publication number: CN111464149A
Application number: CN201910047260.7A
Authority: CN
Inventors: 詹义贤; 郭国仁; 黄朝忠
Original assignee: UPI Semiconductor Corp
Current assignee: UPI Semiconductor Corp
Priority date: 2019-01-18
Filing date: 2019-01-18
Publication date: 2020-07-28
Anticipated expiration: 2039-01-18
Also published as: CN111464149B

Abstract

The invention provides a filter amplifier, which comprises an amplifier circuit and a control circuit. The amplifier circuit includes a first amplifier and a first transistor. The first terminal of the first transistor is coupled to the first input terminal of the first amplifier. The control circuit comprises a second amplifier, a second transistor and a resistor. The first end of the second transistor is coupled to the first input end of the second amplifier. The control end of the second transistor is coupled with the output end of the second amplifier and the control end of the first transistor. One end of the resistor is coupled to the first input end of the second amplifier. Therefore, the filter amplifier of the invention can provide wider filtering frequency range and accurate filtering function.

Description

Filter amplifier

Technical Field

The present invention relates to amplifier circuits, and more particularly, to a filter amplifier.

Background

In the conventional filter amplifier circuit architecture, since the traditional resistor element collocated with the amplifier has a large area and cannot achieve a maximum or minimum resistance value, the filter frequency band of the filter amplifier is limited, and therefore, the specific operating characteristics of the transistor is usually used as a dummy resistor (pseudo-resistor) to be applied to the resistor element of the filter amplifier. However, the method of using the transistor as the dummy resistor still cannot accurately control the resistance value to accurately control the filtering frequency band of the filter amplifier. Therefore, how to extend the filtering band of the filter amplifier and effectively improve the accuracy of the filter amplifier is a problem addressed in the industry.

Disclosure of Invention

The invention provides a filter amplifier, which can expand the filtering frequency band of the filter amplifier and effectively improve the accuracy of the filter amplifier.

The filter amplifier of the invention comprises an amplifier circuit and a control circuit. The amplifier circuit includes a first amplifier and a first transistor. The first terminal of the first transistor is coupled to the first input terminal of the first amplifier. The control circuit comprises a second amplifier, a second transistor and a resistor. The first terminal of the first transistor is coupled to the first input terminal of the first amplifier. The first end of the second transistor is coupled to the first input end of the second amplifier. The control end of the second transistor is coupled with the output end of the second amplifier and the control end of the first transistor. One end of the resistor is coupled to the first input end of the second amplifier.

In an embodiment of the invention, all corresponding terminals of the first transistor and the second transistor are equipotential. The width-to-length ratio of the first transistor to the second transistor is N: and M. The resistance value of the resistor is R. The equivalent resistance value of the first transistor is R M/N.

In an embodiment of the invention, the first terminal of the first transistor and the first terminal of the second transistor are at the same potential. The second end of the first transistor and the second end of the second transistor are at the same potential.

In an embodiment of the invention, the second input terminal of the first amplifier and the second input terminal of the second amplifier are coupled to the same potential.

In an embodiment of the invention, the control circuit further includes a chopper and a comparator. The chopper is coupled to the first input terminal and the second input terminal of the second amplifier. The chopper is used for exchanging voltage input paths of the first input end and the second input end of the second amplifier. The comparator is coupled with the chopper. The comparator is used for comparing the voltage of the output end of the first amplifier and the voltage of the other end of the resistor so as to generate a switching voltage to the chopper.

In an embodiment of the invention, the second terminal of the first transistor is coupled to the output terminal of the first amplifier. The second terminal of the second transistor is coupled to the output terminal of the first amplifier.

In an embodiment of the invention, the other end of the resistor is coupled to another output voltage corresponding to the output voltage provided by the output terminal of the first amplifier.

In an embodiment of the invention, the first input terminal of the first amplifier receives the input voltage through the second terminal of the first transistor.

In an embodiment of the invention, the other end of the resistor is coupled to another input voltage corresponding to the input voltage received by the first input terminal of the first amplifier through the second end of the first transistor.

In an embodiment of the invention, the amplifier circuit further includes a third transistor and a second control circuit. The first end of the third transistor is coupled to the second input end of the first amplifier. The second control circuit is coupled to the control terminal of the third transistor and provides a control voltage to determine an equivalent resistance value of the third transistor.

Based on the above, the filter amplifier of the present invention can utilize a transistor under a control structure applying an active virtual resistor (active pseudo-resistor) to be equivalent to a resistor in a circuit structure of the filter amplifier, so as to provide a wider filtering frequency band and an accurate filtering function.

In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.

Drawings

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

FIG. 1 is a circuit schematic of a filter amplifier according to an embodiment of the invention;

FIG. 2 is a circuit schematic of a control circuit according to an embodiment of the invention;

FIG. 3 is a circuit schematic of a filter amplifier according to another embodiment of the invention;

FIG. 4 is a circuit schematic of a control circuit according to another embodiment of the present invention;

FIG. 5 is a circuit schematic of a differential filter amplifier circuit according to an embodiment of the present invention;

FIG. 6 is a circuit diagram of the control circuit according to the embodiment of FIG. 5;

fig. 7 is a circuit schematic of an inverting amplifier circuit according to an embodiment of the invention.

Detailed Description

In order that the present disclosure may be more readily understood, the following specific examples are given as illustrative of the invention which may be practiced in various ways. Further, wherever possible, the same reference numbers will be used throughout the drawings and the description to refer to the same or like parts.

Fig. 1 is a circuit schematic diagram of a filter amplifier according to an embodiment of the invention. Referring to fig. 1, a filter amplifier 100 includes an amplifier circuit 110 and a control circuit 120. The amplifier circuit 110 includes an amplifier 111, a transistor 112, and a capacitor 113. A first terminal of the transistor 112 is coupled to the input terminal of the amplifier 111, and a second terminal of the transistor 112 is coupled to the output terminal of the amplifier 111. A first terminal of the capacitor 113 is coupled to the first input terminal of the amplifier 111, and a second terminal of the capacitor 113 is coupled to the output terminal of the amplifier 111. A first input terminal of the amplifier 111 receives an input voltage V_INAnd the output of the amplifier 111 provides an output voltage V_OUT. The control terminal of the transistor 112 receives the control voltage V_G. In the present embodiment, the transistor 112 is used to realize a control structure of an active dummy resistor (active dummy). When the three-terminal voltage of the transistor 112 is fixed by the control circuit 120, the virtual resistance (pseudo-resistor) of the transistor 112 can be adjusted by the resistor 123, so that the amplifier circuit 110 can provide the input voltage V to the input circuit_INThe filtering is stably performed.

Control ofThe circuit 120 includes an amplifier 121, a transistor 122, and a resistor 123. A first terminal of the transistor 122 is coupled to a first input terminal of the amplifier 121 to form a feedback path (e.g., negative feedback), and a second terminal of the transistor 122 is coupled to an output terminal of the amplifier 111. Transistor 112 is matched to transistor 122. A control terminal of the transistor 122 is coupled to the output terminal of the amplifier 121, and an output terminal of the amplifier 121 is coupled to a control terminal of the transistor 112 and a control terminal of the transistor 122. The output of the amplifier 121 provides a control voltage V_GTo the control terminal of transistor 112 and to the control terminal of transistor 122. In one embodiment, the resistor 123 is a variable resistor (variable resistor). One end of the resistor 123 is coupled to the first input terminal of the amplifier 121, and the other end of the resistor 123 receives another output voltage V_OUTN. A second input of the amplifier 121 is coupled to a second input of the amplifier 111. In the present embodiment, the second terminal of the transistor 112 and the second terminal of the transistor 122 both receive the output voltage V provided by the output terminal of the amplifier 111_OUTTherefore, the second terminal of the transistor 112 and the second terminal of the transistor 122 are at the same potential.

The

transistors

112, 122 can be N-type transistors or P-type transistors, and the invention is not limited to the type of the

transistors

112, 122. In one embodiment, the

transistors

112 and 122 can be, for example, N-type Metal Oxide Semiconductor (NMOS) transistors or P-type Metal Oxide Semiconductor (PMOS) transistors.

In the present embodiment, the first input terminal of the amplifier 111 has a first voltage V_AAnd a second input terminal of the amplifier 111 has a second voltage V_CM(common mode voltage). The first input terminal of the amplifier 121 has a third voltage V_B. Since the second input terminal of the amplifier 111 is coupled to the second input terminal of the amplifier 121, the second input terminal of the amplifier 111 and the second input terminal of the amplifier 121 are at the same potential, e.g., have the second voltage V_CM. In contrast, the filter amplifier 100 of the present embodiment corresponds to the following equations (1) to (2), and the transistor 122 and the resistor 123 correspond to the following equations (3) to (5).

V_A＝V_CM＝V_B………………………(1)

|V_OUT-V_CM|＝|V_CM-V_OUTN|………………………(2)

V_R＝V_DS………………………(3)

I_R＝I_DS………………………(4)

R＝R_DS2………………………(5)

In the above equation (1), the first voltage V_AA second voltage V_CMAnd a third voltage V_BAre the same. In the above formula (2), the output voltage V_OUTAnd a first voltage V_A(equivalent to the second voltage V_CM) The subtracted absolute value is equal to the first voltage V_AAnd a further output voltage V_OUTNThe absolute value after subtraction. In other words, the other output voltage V of the present embodiment_OUTNCan be designed to make and output the voltage V_OUTCorrelation, the voltage relation of which is, for example, V_OUT<V_CM<V_OUTNOr V_OUT>V_CM>V_OUTNAnd satisfies the above formula (2). In the above formula (3), the voltage V across the resistor 123_RIs equal to the voltage V across the transistor 122_DS. In the above formula (4), the current value I passing through the resistor 123_REqual to the current value I through transistor 122_DS. In the above equation (5), the resistance value R of the resistor 123 is equal to the equivalent resistance value R of the transistor 122_DS2。

Based on the above equations (1) - (5) and the circuit architecture of the filter amplifier 100, it can be further deduced that the transistor 112 and the transistor 122 have the same voltage V_DS. Therefore, the aspect ratio (W) of the transistor 112 is as shown in the following equation (6)₁/L₁) Aspect ratio (W) to transistor 122₂/L₂) Is N: m, and the equivalent resistance value R of the transistor 112_DS1Equivalent resistance value R of the transistor 122_DS2The proportional relation is N: and M. In other words, since the width-to-length ratio of the transistor 112 to the transistor 122 is N: m, and thus the equivalent resistance of the transistor 112 is R × M/N. In the present embodiment, the resistance value R of the resistor 123, the transistor112 and transistor 122 will conform to equation (7) below.

Accordingly, the virtual resistance of the transistor 112 of the present embodiment is related to the resistance of the resistor 123 and the aspect ratio of the transistor 112 to the transistor 122. In other words, the user can design the resistance value R of the resistor 123, the aspect ratio N of the transistor 112, and the aspect ratio M of the transistor 122 to obtain any desired equivalent resistance value R of the transistor 112_DS1So that the transistor 112 can be equivalent to a maximum or minimum resistance value after being designed, and the equivalent resistance value R of the transistor 112 can be precisely controlled by controlling the three-terminal voltage of the transistor 122_DS1The effect of (1).

Fig. 2 is a circuit schematic diagram of a control circuit according to an embodiment of the invention. Referring to fig. 2, the control circuit 220 of fig. 2 is an embodiment of another control circuit suitable for use in the filter amplifier 100 of fig. 1. In this embodiment, the control circuit 220 includes an amplifier 221, a transistor 222, a resistor 223, a chopper (chopper)224, and a comparator 225. Transistor 112 of fig. 1 is matched to transistor 222. A first terminal of the transistor 222 is coupled to a first input terminal of the amplifier 221, and a second terminal of the transistor 222 is coupled to the output voltage V of the amplifier circuit 110 shown in fig. 1_OUT. The control terminal of the transistor 222 is coupled to the output terminal of the amplifier 221, and the output terminal of the amplifier 221 is coupled to the control voltage V of the amplifier circuit 110 shown in FIG. 1_GAnd a control terminal of transistor 222. The output of amplifier 221 provides a control voltage V_GTo the control terminal of transistor 222. One end of the resistor 223 is coupled to the first input terminal of the amplifier 221, and the other end of the resistor 223 receives another output voltage V_OUTN. The second input terminal of the amplifier 221 is coupled to the second voltage V as shown in FIG. 1_CM. The first input terminal and the second input terminal of the amplifier 221 are equipotentialE.g. having a third voltage V_B。

In the present embodiment, the chopper 224 is coupled to the first input terminal and the second input terminal of the amplifier 221. The chopper 224 is used for switching the voltage input paths of the first input terminal and the second input terminal of the amplifier 221. The comparator 225 is coupled to the chopper 224. The comparator 225 is used to compare the output voltage V of the amplifier circuit 110 shown in FIG. 1_OUT(i.e., the output of amplifier 111) and the voltage at the other end of resistor 223 to generate the switching voltage SE L to chopper 224_INIs a time-varying voltage signal, e.g. a sine wave signal, and thus the output voltage V of the amplifier circuit 110 of FIG. 1_OUTMay be higher or lower than the second voltage V_CM. In this regard, the chopper 224 may correspond to a circuit path that switches the first input terminal and the second input terminal of the amplifier 221.

Specifically, the input voltage V as received by the amplifier circuit 110 of FIG. 1_INMay be derived from, for example, an Electrocardiogram (ECG) signal, and thus the comparator 225 may be based on the output voltage V output by the amplifier circuit 110 of fig. 1_OUTThe first input terminal and the second input terminal of the amplifier 221 are switched in real time to maintain the feedback path. Moreover, the control circuit 220 of the present embodiment is combined with the amplifier circuit 110 of fig. 1 and conforms to the equations (1) to (7), so that the detailed descriptions of the equations (1) to (7) can be referred to and analogized from the teaching of the embodiment of fig. 1, and will not be described again here.

Fig. 3 is a circuit schematic diagram of a filter amplifier according to another embodiment of the invention. Referring to fig. 3, the filter amplifier 300 includes an amplifier circuit 310 and a control circuit 320. The amplifier circuit 310 includes an amplifier 311, a transistor 312, and a capacitor 313. A first terminal of the transistor 312 is coupled to the input terminal of the amplifier 311, and a second terminal of the transistor 312 receives the input voltage V_IN. A first terminal of the capacitor 313 is coupled to a first input terminal of the amplifier 311, and a second terminal of the capacitor 313 is coupled to an output terminal of the amplifier 311. A first terminal of the resistor 314 is coupled to a first input terminal of the amplifier 311, and a second terminal of the resistor 314 is coupled to an output terminal of the amplifier 311. First of amplifier 311An input terminal receives an input voltage V via a transistor 312_INAnd the output terminal of the amplifier 311 provides the output voltage V_OUT. The control terminal of the transistor 312 receives the control voltage V_G. In the present embodiment, the transistor 312 is used to realize a control structure of the active dummy resistor. When the three-terminal voltage of the transistor 312 is fixed by the control circuit 120, the virtual resistance of the transistor 312 can be adjusted by the resistor 323, so that the amplifier circuit 310 can provide the input voltage V_INThe filtering is stably performed.

The control circuit 320 includes an amplifier 321, a transistor 322, and a resistor 323. A first terminal of the transistor 322 is coupled to a first input terminal of the amplifier 321 to form a feedback path, and a second terminal of the transistor 322 is coupled to a first input terminal of the amplifier 311. Transistor 312 is matched to transistor 322. A control terminal of the transistor 322 is coupled to the output terminal of the amplifier 321, and an output terminal of the amplifier 321 is coupled to the control terminal of the transistor 312 and the control terminal of the transistor 322. The output of the amplifier 321 provides a control voltage V_GTo the control terminal of transistor 312 and to the control terminal of transistor 322. In one embodiment, the resistor 323 is an adjustable resistor. One end of the resistor 323 is coupled to the first input terminal of the amplifier 321, and the other end of the resistor 323 receives another input voltage V_INN. The other input voltage V of the present embodiment_INNCan be designed to match the input voltage V_INCorrelation, the voltage relation of which is, for example, V_IN<V_CM<V_INNOr V_IN>V_CM>V_INNAnd satisfies the following formula (8). A second input of the amplifier 321 is coupled to a second input of the amplifier 311. In the present embodiment, the second terminal of the transistor 312 and the second terminal of the transistor 322 both receive the output voltage V provided by the output terminal of the amplifier 311_OUTTherefore, the second terminal of the transistor 312 is at the same potential as the second terminal of the transistor 122.

|V_IN-V_CM|＝|V_CM-V_INN|………………………(8)

In this embodiment, the first input terminal of the amplifier 311 has the first voltage VA, and the second input terminal of the amplifier 311 has the second voltage VATwo voltages V_CM(common mode voltage). The first input terminal of the amplifier 321 has a third voltage V_B. Since the second input terminal of the amplifier 311 is coupled to the second input terminal of the amplifier 321, the second input terminal of the amplifier 311 and the second input terminal of the amplifier 321 are at the same potential, e.g., have the second voltage V_CM. In this regard, the filter amplifier 300 of the present embodiment can be analogized to the results of the above equations (1) to (7), so that the electrical characteristics of the filter amplifier 300 can refer to the description of the embodiment of fig. 1, and are not repeated herein. Accordingly, a user can design the resistance of the resistor 323, the aspect ratio of the transistor 312, and the aspect ratio of the transistor 322 to obtain any desired equivalent resistance of the transistor 312, so that the transistor 312 can be equivalent to a maximum or minimum resistance after being designed, and the equivalent resistance R of the transistor 312 can be precisely controlled by controlling the three-terminal voltage of the transistor 322_DS1The effect of (1).

Fig. 4 is a circuit schematic of a control circuit according to another embodiment of the invention. With reference to figure 4 of the drawings,

the control circuit 420 of fig. 4 is an embodiment of another control circuit suitable for use in the filter amplifier 300 of fig. 3. In this embodiment, the control circuit 420 includes an amplifier 421, a transistor 422, a resistor 423, a chopper 424, and a comparator 425. Transistor 312 of fig. 3 is matched to transistor 422. A first terminal of the transistor 422 is coupled to a first input terminal of the amplifier 421, and a second terminal of the transistor 422 is coupled to an input voltage V of the amplifier circuit 310 of fig. 3_IN. The control terminal of the transistor 422 is coupled to the output terminal of the amplifier 421, and the output terminal of the amplifier 421 is coupled to the control voltage V of the amplifier circuit 310 of FIG. 3_GAnd a control terminal of transistor 422. The output terminal of the amplifier 421 provides the control voltage V_GTo the control terminal of transistor 422. One end of the resistor 423 is coupled to the first input terminal of the amplifier 421, and the other end of the resistor 423 receives another input voltage V_IN. The second input terminal of the amplifier 421 is coupled to the second voltage V as shown in FIG. 3_CM. The first input terminal and the second input terminal of the amplifier 421 are equipotential, e.g. have a third voltage V_B。

In the present embodiment, the chopper 424 is coupled to the first input terminal and the second input terminal of the amplifier 421. The chopper 424 is used for switching the voltage input paths of the first input terminal and the second input terminal of the amplifier 421. The comparator 425 is coupled to the chopper 424. The comparator 425 is used to compare the input voltage V of the amplifier circuit 310 of FIG. 3_IN(i.e., the input of amplifier 311) and the voltage at the other end of resistor 423 to generate the switching voltage SE L to chopper 424_INIs a time-varying voltage signal, e.g. a sine wave signal, and thus the input voltage V of the amplifier circuit 310 of FIG. 3_INMay be higher or lower than the second voltage V_CM. In this regard, the chopper 424 may correspond to a circuit path for switching the first input terminal and the second input terminal of the amplifier 421.

Specifically, the input voltage V as received by the amplifier circuit 310 of FIG. 3_INMay be derived, for example, from an electrocardiogram signal, so that the comparator 425 may be based on the output voltage V as output by the amplifier circuit 310 of fig. 3_OUTThe first input terminal and the second input terminal of the amplifier 421 are switched in real time to maintain the feedback path. Moreover, after the control circuit 420 of the present embodiment is combined with the amplifier circuit 310 of fig. 3, the results of the above equations (1) to (7) can be analogized, so that the related electrical characteristics thereof can refer to the description of the embodiment of fig. 1, and are not repeated herein.

FIG. 5 is a circuit diagram of a differential filter amplifier circuit according to an embodiment of the invention. FIG. 6 is a circuit diagram of the control circuit according to the embodiment of FIG. 5. Referring first to fig. 5, the differential filter amplifier circuit 510 includes a differential filter amplifier 511, transistors 512 and 514,

capacitors

513 and 515, and

input capacitors

516 and 517. A first terminal of the transistor 512 is coupled to a first input terminal of the differential filter amplifier 511, and a second terminal of the transistor 512 is coupled to a first output terminal of the differential filter amplifier 511. The first output terminal of the differential filter amplifier 511 provides an output voltage V_OUTP. One end of the capacitor 513 is coupled to the first input terminal of the differential filter amplifier 511, and the other end of the capacitor 513 is coupled to the first output terminal of the differential filter amplifier 511. Of transistors 514A first terminal is coupled to the second input terminal of the differential filter amplifier 511, and a second terminal of the transistor 514 is coupled to the second output terminal of the differential filter amplifier 511. The second output terminal of the differential filter amplifier 511 provides the output voltage V_OUTN. One end of the capacitor 515 is coupled to the second input terminal of the differential filter amplifier 511, and the other end of the capacitor 515 is coupled to the second output terminal of the differential filter amplifier 511. One end of the input capacitor 516 is coupled to the first input terminal of the differential filter amplifier 511, and the other end of the input capacitor 516 receives the first input voltage V_IN. One end of the input capacitor 517 is coupled to the second input terminal of the differential filter amplifier 511, and the other end of the input capacitor 517 receives the second input voltage V_IP. The control terminal of the transistor 512 receives a first control voltage V_G1And the control terminal of the transistor 514 receives the second control voltage V_G2。

Referring next to fig. 6, a control circuit 620 may be adapted for use with the differential filter amplifier circuit 510 of fig. 5. Control circuit 620 includes

amplifiers

621, 624,

transistors

622, 625, and

resistors

623, 626. Transistor 622 is matched to transistor 512 of fig. 5. A first terminal of the transistor 622 is coupled to a first input terminal of the amplifier 621 to form a feedback path, and a second terminal of the transistor 622 is coupled to a first output terminal of the amplifier 511 shown in fig. 5. The control terminal of the transistor 622 is coupled to the output terminal of the amplifier 621, and the output terminal of the amplifier 621 is coupled to the control terminal of the transistor 512 and the control terminal of the transistor 622 in fig. 5. The output terminal of the amplifier 621 provides the control voltage V_G1To the control terminal of transistor 512 and to the control terminal of transistor 622 as shown in fig. 5. In one embodiment, resistor 623 is an adjustable resistor. One end of the resistor 623 is coupled to the first input terminal of the amplifier 621, and the other end of the resistor 623 receives the output voltage V_OUTP. The second input of amplifier 621 receives a second voltage V_CM。

Transistor 625 is matched to transistor 514 of fig. 5. A first terminal of transistor 625 is coupled to a first input terminal of amplifier 624 to form a feedback path, and a second terminal of transistor 625 is coupled to a second output terminal of amplifier 511 of fig. 5. A control terminal of transistor 625 is coupled to the output terminal of amplifier 624, and amplifier 6An output terminal of 24 is coupled to a control terminal of the transistor 514 and a control terminal of the transistor 625 of fig. 5. The output of amplifier 624 provides a control voltage V_G2To the control terminal of transistor 514 and to the control terminal of transistor 625 as shown in figure 5. In one embodiment, resistor 626 is an adjustable resistor. One end of the resistor 626 is coupled to the first input terminal of the amplifier 624, and the other end of the resistor 626 receives the output voltage V_OUTN. A second input of the amplifier 624 receives a second voltage V_CM. Accordingly, the filter amplifier composed of the amplifier circuit 510 of fig. 5 and the control circuit 620 of fig. 6 can be analogized to the above equations (1) to (7), so that the detailed descriptions of the equations (1) to (7) can be referred to and analogized to the teaching of the embodiment of fig. 1, and will not be repeated herein.

The dummy resistance of the transistor 512 of this embodiment is related to the resistance of the resistor 623 and the aspect ratio of the transistor 512 to the transistor 622. In other words, a user can design the resistance of the resistor 623, the aspect ratio of the transistor 512, and the aspect ratio of the transistor 622 to obtain any desired equivalent resistance of the transistor 512, so that the transistor 512 can be equivalent to a maximum or minimum resistance after being designed, or the equivalent resistance of the transistor 512 can be precisely controlled. Similarly, the virtual resistance of the transistor 514 of the present embodiment is related to the resistance of the resistor 626 and the aspect ratio of the transistor 514 to the transistor 625. In other words, the user can design the resistance value of the resistor 626, the aspect ratio of the transistor 514, and the aspect ratio of the transistor 625 to obtain any desired equivalent resistance value of the transistor 514, so that the transistor 514 can be equivalent to a very large resistance value after being designed, and the effect of precise control can be achieved by controlling the equivalent resistance value of the transistor 514.

Furthermore, the common mode voltage and the two terminals of the first output terminal and the second output terminal of the differential filter amplifier circuit 510 may be completely corresponding voltages. In other words, compared to the output voltage V received by the resistor 123 coupled to the first input terminal of the amplifier 121 of the control circuit 120 in the embodiment of fig. 1_OUTNCan be designed to make and output the voltage V_OUTIn connection with this, the amplifier of the control circuit 620 of the present embodimentThe resistor 623 coupled to the first input terminal of the transistor 621 can directly receive the output voltage V provided by the second output terminal of the transistor 511_OUTNMoreover, the resistor 626 coupled to the first input terminal of the amplifier 624 of the control circuit 620 of the present embodiment can directly receive the output voltage V provided by the first output terminal of the transistor 511_OUTPTo generate a control voltage V_G1、V_G2. In the present embodiment, the output voltage V_OUTNAnd an output voltage V_OUTPIs for example V_OUTN<V_CM<V_OUTPOr V_OUTN>V_CM>V_OUTP。

Fig. 7 is a circuit schematic of an inverting amplifier circuit according to an embodiment of the invention. Referring to fig. 7, the inverting amplifier circuit 710 includes an amplifier 711,

transistors

712, 713, and a capacitor 714. In this embodiment, a first terminal of the transistor 712 is coupled to a first input terminal of the amplifier 711, and a second terminal of the transistor 712 is coupled to an output terminal of the amplifier 711. The control terminal of the transistor 712 receives the control voltage V_G1'. A first terminal of the transistor 713 is coupled to a first input terminal of the amplifier 711, and a second terminal of the transistor 713 receives the input voltage V_IN. The control terminal of the transistor 713 receives the control voltage V_G2'. A first terminal of the capacitor 714 is coupled to a first input terminal of the amplifier 711, and a second terminal of the capacitor 714 is coupled to an output terminal of the amplifier 711. The second input terminal of the amplifier 711 receives the second voltage V_CM(common mode voltage) and the output of the amplifier 711 provides an output voltage V_OUT。

The control method and the circuit connection method of the transistor 712 of the present embodiment can be matched with the circuit architectures of the

control circuits

120 and 220 of the embodiments of fig. 1 and 2, and the control method and the circuit connection method of the transistor 713 of the present embodiment can be matched with the circuit architectures of the

control circuits

320 and 420 of the embodiments of fig. 3 and 4. In other words, at least one of the feedback resistance (equivalent to the feedback resistance by controlling the transistor 712) of the inverting amplifier circuit 710 and the input resistance (equivalent to the input resistance by controlling the transistor 713) of the input terminal of the present embodiment can be applied to the control structure of the active dummy resistance provided in the above embodiments of the present invention, so as to achieve the effect that the

transistors

712 and 713 can be equivalent to the maximum resistance value after being designed, or the effect of precisely controlling the equivalent resistance values of the

transistors

712 and 713 can be achieved. For the coupling manner and the implementation details of the circuit elements of the amplifier circuit 710, reference may be made to the above description of the embodiment of fig. 1 to 6, so as to obtain sufficient teaching, suggestion and implementation description, and therefore, the description thereof is not repeated herein.

In summary, the filter amplifier of the present invention can utilize the transistor to be equivalent to at least one of the feedback resistor and the input resistor in the amplifier circuit, determine the equivalent resistance of the controlled transistor by adjusting the width-to-length ratio of the resistor in the control circuit and the other transistor, and precisely control the equivalent resistance of the dummy resistor in the amplifier circuit by controlling the three-terminal voltage of the other transistor in the control circuit. Therefore, the filter amplifier of the invention can obtain any required resistance value and can provide accurate voltage signals so as to provide wider filter frequency band and accurate filter function.

Although the present invention has been described with reference to the above embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A filter amplifier, comprising:

an amplifier circuit, comprising:

a first amplifier; and

a first transistor, a first terminal of which is coupled to the first input terminal of the first amplifier; and

a control circuit, comprising:

a second amplifier;

a second transistor, a first terminal of which is coupled to the first input terminal of the second amplifier, and a control terminal of which is coupled to the output terminal of the second amplifier and the control terminal of the first transistor; and

and one end of the resistor is coupled with the first input end of the second amplifier.

2. The filter amplifier of claim 1, wherein all respective ends of the first transistor and the second transistor are equipotential, and wherein a width-to-length ratio of the first transistor to the second transistor is N: and M, the resistance value of the resistor is R, and the equivalent resistance value of the first transistor is R M/N.

3. The filter amplifier according to claim 1, wherein the first terminal of the first transistor and the first terminal of the second transistor are at the same potential, and the second terminal of the first transistor and the second terminal of the second transistor are at the same potential.

4. The filter amplifier of claim 1, wherein the second input of the first amplifier and the second input of the second amplifier are coupled to the same potential.

5. The filter amplifier of claim 1, wherein the control circuit further comprises:

a chopper coupled to the first and second inputs of the second amplifier and configured to switch voltage input paths of the first and second inputs of the second amplifier; and

the comparator is coupled to the chopper and used for comparing the voltage of the output end of the first amplifier and the voltage of the other end of the resistor so as to generate a switching voltage to the chopper.

6. The filter amplifier of claim 1, wherein a second terminal of the first transistor is coupled to the output of the first amplifier, and wherein the second terminal of the second transistor is coupled to the output of the first amplifier.

7. The filter amplifier of claim 6, wherein the other end of the resistor is coupled to another output voltage corresponding to an output voltage provided by the output of the first amplifier.

8. The filter amplifier of claim 1, wherein the first input of the first amplifier receives an input voltage via a second terminal of the first transistor.

9. The filter amplifier of claim 8, wherein the other end of the resistor is coupled to another input voltage corresponding to the input voltage received by the first input of the first amplifier via the second end of the first transistor.

10. The filter amplifier of claim 1, wherein the amplifier circuit further comprises:

a third transistor, a first end of which is coupled to the second input end of the first amplifier; and

the second control circuit is coupled to the control terminal of the third transistor and provides a control voltage to determine an equivalent resistance value of the third transistor.